In many industrial environments arc welders are used to weld a seam between two workpieces of relatively large size. Preferably a guidance system is used in conjunction with the arc welder in order to reduce the manpower necessary and the time required to make the weld.
Ideally, the guidance system should be able to seek the seam in a workpiece, proceed to it quickly and accurately and start to weld. Lapped joints should be able to be welded by the arc welder by using the guidance system, that is, the guidance system should be able to maintain the head of the arc welder in relation to a given side of a joint.
Various guidance systems have been devised in order to automate arc welding. One known guidance system is the Automatic Groove Follower For Welding Apparatus in the Morehead U.S. Pat. No. 3,171,012. That patent discloses a welding head for depositing flux in a groove and means for moving the work and the welding head relative to each other in a direction generally lengthwise with respect to the groove. Motors are used for the horizontal and vertical movement of the welder.
The probe assembly is mounted in front of the welding head and includes an elongated feeler which is pivotally mounted in order that it may open and close various electrical contacts in accordance with the direction in which the feeler is deflected. An appropriate circuit is associated with the contacts to align the welding head with respect to the groove sensed by the elongated feeler.
There are two significant deficiencies in the Morehead apparatus. The elongated feeler is not capable of making horizontal adjustments unless there are two sides to the seam; that is, the elongated feeler must have a path in which it may travel in order to actuate the contacts which move the head of the arc welder in an appropriate direction. This is particularly a problem where there is a lap joint. By lap joint it is meant that one of the workpieces overlaps another workpiece. In this situation it is desirable to lay a bead or seam at the connecting line. However, in the guidance system of Morehead, the feeler would sense the upper workpiece and a signal would be sent to the horizontal motor to move the probe and the arc head away from the actual point where the weld is desired.
A similar problem is encountered where there is a deep groove and overlapping beads are required. The initial seam would work with the Morehead device. A subsequent seam, however, would be erratic due to the fact that the probe would sense both of the sides of the groove and the initial bead, and literally bounce back and forth.
Needless to say, it would be highly desirable to be able to program the probe so that it would abut against one side of the groove in order to signal the arc welder to lay its seam along the precise line desired.
It is also highly desirable if the accompanying circuitry for the guidance system has dynamic braking to prohibit the motors from coasting to a stop and thereby having the probe and arc welder overshoot its target. That is, it is desirable to bring the arc head to its position as quickly as possible and stop it there in order to maintain the necessary accuracy. Multiple speeds for the movement of the probe and welding head are also desirable to improve the efficiency of the operation. In this area the Morehead device is also deficient.
The present invention has the desirable aspects noted above. It provides a probe and accompanying circuitry which can be programmed to move along the edge of an abutment such as a lap joint. That is, the probe is "preloaded" so that it will seek an edge or abutment and once it has reached it, maintain a constant contact with it so that the arc head will lay the bead along the seam. This invention also provides for two-speed step control in bringing the arc head to its desired position and dynamic braking of the motors for precise corrections.